How do you take reference photos?
Use your phone camera, and hold it as far away as possible to reduce lens deformation. Hold the camera so the lens is at eye's height, as centered as possible. Cut the photo in two using gimp or other 2D software, and mirror it. Even professional taken photos have some non symmetricsl details.

Also take a shot in profile, at the same distance and height, and adjust to keep as close as possible the proportions between the two shoots.

Use the reference just as it is: a reference not a sharp point-to-point grid.